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Aftermarket springs vs stock shocks. READ BEFORE POSTING

91K views 50 replies 45 participants last post by  philrab 
#1 ·
EVERYONE should be reading this post. Mod's please sticky.


This is cut and pasted from Joe Cheng in an earlier thread:

For the record, I got into open wheel cars in 1991. Prior to that, it was all production based cars beginning in the ‘70s. If I have to do it all over again, I would have switched earlier.

Now that Zoomee jumped in and asked some good questions (not to mentioned that he is also polite and doesn’t end his sentences with WTF), I will try to put in my two cents (don’t forget this is in Canadian currency now, so it might not worth that much).

First, I would like to confess that up until year and a half ago, I have never heard anyone (and I do hang out with a lot of car guys) use the phrase “…lower springs would blow your OEM shocks….”. It was one of my friend’s son who said it to me while we were discussing his car, and I replied “…what do you mean by blown….”. He then told me that’s what he read on the internet, and he doesn’t quite know what it means either. Fast forward to last November. I bought a Mazda3 for my kids and decided to join this board, hoping to pick up on some useful information on the car. Then I hear all this talk about “blown” OEM shocks caused by lower springs. I posted a message a while back asking what defines a “blown” shock and the thread went quite suddenly. Nobody replied. My message was the last post on the thread and to this day, there is no official definition of a “blown” shock by the internet crowd.

To me, a “blown” shock is a dead shock. A shock that has ZERO damping force. A shock that has been used and has less damping force compare to a new one is a “worn” shock, according to my definition. Like all components on a car, a shock will start wearing with miles. How fast it wears is called “wear rate”. I understand “accelerated wear rate”, I understand “abnormal wear rate”. However, when someone tells me that Prokit can blow my shocks, I take that as Prokit can change my shock’s damping value from some finite value to ZERO within a short instance, similar in context as we would use when we say “blown engine” for example.

For the record, I have had many sets of lower springs over the years on various cars. All of them were driven on the streets or dual-purpose cars (street and competition use). They included Hondas, BMWs, Miata, Mazda3. Some of them have different brands put on over the period I owned them. Two Porsches were lowered using the OEM springs (or torsion bars) since they come factory ride height adjustable. The longest I kept was my wife’s BMW, 17 years on Prokit and one front shock was worn out at the 15 years mark (I won’t call that blown, I call that worn out). All these vehicles have had OEM shocks with the lower springs. The Miata is the only exception, it ran on OEM shocks and lower springs for about 3 years before Tein Flex went on. The OEM shocks were not “blown” when I removed them, yes, I did check.

Now, let’s go on with the technical stuffs (disclaimer: DON’T BELIEVE EVERYTHING YOU READ ON THE INTERNET, INCLUDING THE FOLLOWING).

Zoomee is correct when he wrote “…I suspect that the stronger spring will probably work the OEM shock a little more as it was specifically valved to damp the oscillations of the OEM spring. Increasing the spring rate should create longer duration system vibrations which may generate more energy over the life of the shock….”.

In a damped vibration system, if the damping force is high enough to allow only one oscillation cycle to complete and then come to a complete stop, we call that damping force “critical damping force”. If it allows the body to complete 2 cycles before coming to a rest, then we call it 50% critical damping or 0.5 x CD. Typically, production cars can be anywhere from 0.2 to 0.5x range and there about. Since a shock’s damping forces are rarely linear relative to its speed (shock’s shaft speed, not vehicle speed), the actual damping ratio is not a constant value dynamically. Rest assures, cars like Porsches (in my opinion the only make that has proper shocks straight from the factory) and Corvettes will have a higher damping ratio than your Mazda3. Nevertheless, this design damping ratio is a consideration when springs and shocks are picked for your Mazda3 at the factory. When a stiffer spring is installed. The original damping ratio is lowered. This means the system is under-damped compare to the original set up and the system will take more cycles before coming to rest whenever an external force is applied to it. This means all things equal, the shocks will see a corresponding higher number of cycles in a given fixed time period. However, all things are rarely equal in real life applications. Consider this, while the under-damped system is going thru its extra cycles, but before completing them, another external force is applied to it and this new force is completely out of sync of the vibration. It will actually stop (or cancel out part of) the vibration that is yet to be completed. What does all this mean??? It means if the system is 20% under-damped, in real life application you might only see part of that 20% come thru as actual increase in wear.

Now, let’s look at the component that is actually causing all the fuss. Since the whole thread started on those Prokit, let’s look at them specifically. In my opinion, the Prokit is the mildest of the milds as far as lowering springs go. They usually range from just less than 10% to somewhere under 20% stiffer than OEM spring rates according to reports from other car forums when people have actually measured the rates (but hey, what did I say about information gathered from the internet). I would say they usually average around 12-15%, give and take a few percent. Therefore, if we put Prokit on, there should be a corresponding “accelerated wear rate” on the shocks, but “blowing” the shocks (see my definition earlier), I doubt it. Now, assume your OEM shocks typically have a life span of say 5 years, so what if that 5 years decrease to 4 years. Are you going to cry over it? Maybe the OEM shocks on the Mazda3 would last 10 years without Prokit and that will get shortened to 8 years if you lowered it. Are you going to cry over that? Don’t forget, my wife’s lasted 15 years. If the OEM shocks are that bad as someone here reported “blowing” them within 6 months, then I am pretty sure those shocks wouldn’t have lasted much longer with the OEM springs anyway.

So far, I have only talked about increased spring rate. Now, let’s see what happens when the ride height is lowered.

One common characteristic of all typical automotive shocks is that they are all velocity sensitive (again, I am talking about shock shaft velocity, not vehicle velocity) rather than displacement sensitive. Zoomee is correct when he wrote “…The lowered condition causes the shock piston to ride in a slightly different location proportionate to the amount of lowering which shouldn't cause any real problems with shock absorber life….”. The only exception is some of those self-leveling shocks and a recent report on a shock which is displacement sensitive, but these are different animals compare to what we are talking about here.

For some cars, there is a lot of suspension travel from the factory. For some other cars, there is minimal. The Mazda3 is not bad. I lowered mine 1.7” and there is still travel left (not much though). I can’t say the same thing about my Miata’s rear. The problem with limited travel is that some owners end up cutting down their bump stops to gain extra travel. Once the shock’s internals touch, you will get a “blown” shock (as in going to zero damping right now). Some owners don’t cut their bumpstop and over time, the bumpstop actually disintegrates due to fatigue from being squished all the time. The hard rubber ones on Japanese cars are not bad; they last longer than the European ones which are typically made out of urethane foam rubber similar to Koni’s silasto bumpstop. They give a much more progressive rate, cushioning the bottoming action. This usually fools the owners, and when the bump stops finally wear to a certain point, instant blown shock results when a big bump is hit due to internal contact. For the Mazda3, there is more than adequate travel left before bottoming on the bump rubber if we are only talking about 1.2 to 1.5 inch of drop. As I said earlier, Prokit is the mildest of the mild in terms of both rate and ride height change. Not an issue in my opinion. For other applications where extreme amount is taken out of the suspension travel, and contact with the bumpstop is a routine thing, then the only solution is to use a shortened shock or raise the shaft above its original mounting height at the chassis end.

As to ride quality, there is not much one can do about it. Stiffer springs come with a corresponding stiffer ride. However, having driven many cars with Prokit, the only comment I can say is that for all of you who complain about the Prokit ride, I hope none of you lust after cars like Porsches, Corvettes and Ferraris because they all ride noticably harsher. And for those who are concerned about having to take a steep ramp at an angle, all I can say is my stock ride height NSX and Corvette both had more trouble because of their large front overhangs than my others cars with lower springs. If you want ground clearance, buy an SUV. If you want a plush ride, I highly recommend my last mini van, the Toyota Sienna. But seriously folks, compare to a mild increase in spring rate like the Prokit, tire and wheel packages can ruin the ride much easier.
 
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#5 ·
Good read. I compliment you on your ability to explain this difference between aftermarket springs vs stock.

I do laugh not at you but with in in how you wrote "You cannot beleive everything you read on the internet." because this is also on the internet. But, looking at the information presented to me, I trust you.
 
#7 ·
I just did a search to find this sticky and man am I glad i did . This guys knows his stuff. I was totally confused until i read this information. Great read and should be read by anyone even remotely thinking about lowering their car. Thanks for making this info available . ............... Clue
 
#8 ·
I just wanna know what I should do to get the best performance on my 2006 i Touring.
Prioritize so I can economize, does that make sense? I am not sure even after reading the below,
what route to take. Even though the below is a good read.

So was he saying that lowering springs is best if you pick the right dampening for the vehicle to use with OEM tires, wheels and shocks?
i got confused there
 
#9 ·
A nice tidbit extracted about of the original post can also be attributed to what I believe others refer to as "Eibounce" (bouncy ride on Eibach springs...or other aftermarket lowering springs for that matter) where the car has a bouncy ride due to performance lowering springs being paired with stock/oem shocks and struts.

...this design damping ratio is a consideration when springs and shocks are picked for your Mazda3 at the factory. When a stiffer spring is installed. The original damping ratio is lowered. This means the system is under-damped compare to the original set up and the system will take more cycles before coming to rest whenever an external force is applied to it. This means all things equal, the shocks will see a corresponding higher number of cycles in a given fixed time period. However, all things are rarely equal in real life applications. Consider this, while the under-damped system is going thru its extra cycles, but before completing them, another external force is applied to it and this new force is completely out of sync of the vibration. It will actually stop (or cancel out part of) the vibration that is yet to be completed.
I think the moral of the story here is to have "properly matched" springs and struts/dampers so they won't be operating at different "cycles" in response to forces exerted upon them. OEM struts may be fine with aftermarket springs for durability-sake for most people, but they may not be ideally matched, rate-wise...imo.

-halo
 
#12 ·
I have the Eibach Prokit and have no such bounce. The springs are reactive to the bumps you go over but I would say that the rebound is much tighter than the compression. Just my observations. I love the springs and I will change out the shocks and struts when they go but for now i think they are fine. ............ Clue
 
#15 ·
This is very usefull information, but i didn't get one thing, the bumpstops, they have to be cut at the time of Proline springs installation? or should they not? which is better to do to mmet these springs with oem shocks? I have installed H&R Sport springs on my old Corolla, cut bumpstops a half size, stock shocks, and the ride was not even bumpy but handling was awasome, but i think if i wouldn't cut the bumpstop then most likely i have some problem with really hard and harsh ride.
 
#18 ·
Ok, i have read online as someone here on this forum has instructions on "HOW TO INSTALL PRO KIT Springs", i have noticed nothing was mentioned about bump stops, so i figured i do not need to cut them, Honestlly i tried but they WERE NOT ABLE TO be cut, so i figure i won't use bigger scissors, juet let it go like that, installed Pro kit, ride is AWASOME, and DO NOT CUT your bump stops, bump stops are made to stop your car traveling down from hitting the ground when you go over a high hill at really fast speed, with the stop bump it is noticable at 70 mph going over a little inclining bump, but anything below that it will never reach the bump stop, so no worries about a bump stop for Mazda3.
 
#20 ·
[quote author=sanmaz3_84 link=topic=21461.msg947579#msg947579 date=1158099617]
i was thinkin of lowering my mazda 3 aswell but not by means of a kit, but rather by cutting em myself?!?!?
[/quote] :blitz:
Honestly man- why would you ever do that? Your gunna save a couple bucks... now... Your not going to be able to get a perfectly level ride by cutting them (well, not by doing it just once probably)- its going to feel like crap- your going to hit your bump stops constantly, as a result youll blow your shocks out INCREDIBLY fast and have to replace them (way more expensive than a kit)- and your not going to have your OEM springs if ever a suspension problem arises under warranty, or you want to sell/trade in your car.

Suck it up and either dont do it, or spend the money for good quality springs.
 
#21 ·
[quote author=sanmaz3_84 link=topic=21461.msg947579#msg947579 date=1158099617]
i was thinkin of lowering my mazda 3 aswell but not by means of a kit, but rather by cutting em myself?!?!?
[/quote]

:blitz: :blitz: :blitz: :blitz: :blitz: :blitz: :blitz: :blitz: :blitz: :mad: :bash: :grr: :rtfm: :bitching: :nono: :dur:

someone already asked that on a thread and it didn't go very well...
 
#23 ·
I don't want to lower the sled but I'd like some better springs and dampeners.
Who's making something like that? I'm mostly familiar with Penske when it comes to suspension...
Harsh ride? My other car is a Cooper S and I'm a long-distance motorcyclist; I put Traxxion Dynamics suspension mods on the bike.
 
#25 ·
A nice tidbit extracted about of the original post can also be attributed to what I believe others refer to as "Eibounce" (bouncy ride on Eibach springs...or other aftermarket lowering springs for that matter) where the car has a bouncy ride due to performance lowering springs being paired with stock/oem shocks and struts.

Quote
...this design damping ratio is a consideration when springs and shocks are picked for your Mazda3 at the factory. When a stiffer spring is installed. The original damping ratio is lowered. This means the system is under-damped compare to the original set up and the system will take more cycles before coming to rest whenever an external force is applied to it. This means all things equal, the shocks will see a corresponding higher number of cycles in a given fixed time period. However, all things are rarely equal in real life applications. Consider this, while the under-damped system is going thru its extra cycles, but before completing them, another external force is applied to it and this new force is completely out of sync of the vibration. It will actually stop (or cancel out part of) the vibration that is yet to be completed.


I think the moral of the story here is to have "properly matched" springs and struts/dampers so they won't be operating at different "cycles" in response to forces exerted upon them. OEM struts may be fine with aftermarket springs for durability-sake for most people, but they may not be ideally matched, rate-wise...imo.

-halo
so in response to this. which is exactly what i have sort of been looking for in regards to an answer..... i have some other opnions as to why mailed to me by a friend of mine.

the advantages to coilovers are that you can run much higher spring rates because the shocks/struts that come with it are valved stiff enough. you also get adjustable height. most coilovers also offer stiffer springs than you can find when just buying springs.

for example for the miata i'm running a 394 lb/in front spring and a 330 lb/in rear spring. the highest rate springs that fit the stock shocks are 318/233.

the next problem with running stock shocks is when you lower the car, you lose suspension travel. basically your drop is eating into your suspension travel. also depending on how high you go onthe spring rates it may not be able to handle it. basically you'll get a crashy/jarring ride and less traction on the track.

coilovers fix this, they have shorter than stock shock/strut bodies. so you maintain all your suspension travel while dropping the car. and design their valving to match their spring rates.

you can get just springs and run your stock shocks/struts, if you dont increase the spring rate too high over the stock spring rate and are conservative on the drop you'll be fine. since you are upgrading the suspension based on track performance, i would save up for a set of coilovers. skip the springs unless you can find some that have a high enough spring rate, but then there's the problem of finding a shock/strut that is valved firm enough for those rates.



my question here is... basically if you dont have a high enough spring for your stock shocks - you will actually get a bouncier ride due to the shock already being compressed and having little to rebound upon?

so. its almost worse to ride tuner springs depending on the stiffness of the original shocks?
 
#26 ·
According to Cobb, a fairly respected name in this business, the factory springs are overmatched by the factory dampers. Their replacement springs are 15% stiffer front and 25% stiffer rear if I remember correctly, and their testing indicates that the factory dampers are a good match for these. In fact, for purchasers of their suspension kits, they recommend keeping the factory struts.
 
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